An agricultural harvester, for example a forage harvester or a combine, is a farm implement that harvests plants, e.g., forage plants to make silage. Silage is grass, corn or other plant that has been chopped into small pieces. Silage can be compacted together in a storage silo, silage bunker or in silage bags. To this end, the harvester is provided to harvest the crop material from a field, to chop the crop material into short pieces, and to expel the chopped pieces (silage) from the harvester into a filling wagon. Modern harvesters are typically self-propelled. The self-propelled harvester is provided with a number of knives fixed on a drum to chop and blow the silage out a chute of the harvester (also referred to as filling spout) into a filling wagon. The filling wagon is typically another vehicle driven alongside the harvester.
In a conventional situation the harvester is operated by a first operator, and the filling wagon is operated by a second operator. Herein, the second operator drives the filling wagon along a path such that the relative position of the filling wagon with respect to the harvester is predetermined (or at least within predetermined boundaries). The first operator (of the forage harvester) operates the filling spout, which is directed to the filling wagon to fill the latter with the chopped crop material. Both the first and the second operator operate based on visual impressions and experience.
In the prior art, for example in US 2003/0174207, it is suggested to use a camera to assist the operators in finding an optimal position of the filling wagon with respect to the forage harvester. Furthermore, the filling spout of the harvester is automatically controlled based on the images from the camera.
A drawback of the known sensor arrangement is that the position of the filling wagon with respect to the forage harvester cannot be determined with a high accuracy in a cost effective manner. With a standard camera, which can be provided at an acceptable cost, the position cannot be determined accurately.